Filter elements are used in many fields of engineering for filtration of a wide variety of dissimilar fluids. Some examples of such fluids include hydraulic fluids, lubricants, and fuels. When the fluid flows through a filter medium of the filter element, an electric voltage can be built up. In worst case scenarios, this electric voltage can assume a value that leads to at least a partial destruction of the filter medium or even the filter element. This situation can arise, especially if the charges, generated during the formation of the voltage, cannot be dissipated in a suitable manner from the filter element. To overcome the problem of the generation of the aforementioned voltages, providing the filter medium with a certain conductivity by, for example, introducing conductive wires and inducing a dissipation of the charges accumulating at the filter medium by suitable—usually metallic—additional filter element components are known. Another requirement of such filter elements is the ability to manufacture them at a low cost and in large quantities. To satisfy the latter requirement, bonding together—for example, by adhesively cementing—the individual components of a filter element is expedient. However, the prior art solutions are often cost-intensive and present a significant recycling problem due to the use of a plurality of dissimilar materials.
DE 10 2007 013 178 A1 discloses a method for producing a filter element of the type described above and comprising the steps: providing a filter medium that surrounds an inner filter cavity and contains a heat sealable material; providing at least one end cap that forms a covering of the filter cavity on at least one end, the end cap being made of a laser transmissive thermoplastic material; forming a laser non-transmissive barrier layer between the end cap and the adjacent end of the filter medium; and welding the end cap and the filter medium by irradiating a laser transmissive material adjacent to the barrier layer, with laser energy such that by heating the region adjacent to the barrier layer, a welding volume is made available as a joining element for the welded joint produced by laser transmission welding. To form the barrier layer, a welding film that is non-transmissive to laser light can be inserted between the end cap and the adjacent end of the filter medium.
Since the filter element components are bonded together by laser light in a transmission welding process, an economical production is ensured. The prior art joins the filter elements to each other with an epoxy resin adhesive. However, in contrast to the laser transmission welding method, this method has many drawbacks. For example, this method has a high space requirement for the reaction accumulators, storage areas for the adhesively cemented filter elements, and the adhesive. In addition, this method is very time-consuming, so that the production costs are correspondingly high. The advantages of laser transmission welding lie in the low thermal and mechanical stress on the associable filter element components that are to be bonded together and in the flexibility of laser transmission welding, as well as the possibility of its automation and integration into existing production sequences. With regard to the financial aspect, the expenses incurred for the adhesive and the reaction accumulators are eliminated. In addition, there are no cleaning costs or maintenance costs, as is the case with cementing. Furthermore, the laser transmission welding process has shorter cycle times.